Olefin homopolymers and copolymers (i.e. polyolefins) have become commercially important for the manufacture of various merchandise. Polyolefins however are often undesirably translucent due to the crystal structure of the polymer. Nucleating agents which enhance nucleation during solidification of molten polymer are thus widely used in polyolefin compositions and particularly polypropylene to improve the clarity, physical properties and value of the polyolefins. Nucleating agents are usually available as solids at room temperature. U.S. Pat. Nos. 3,207,735 and 3,207,738 disclose the use of benzoic acid and aryl alkanoic acid type compounds to improve the properties of polypropylene. The combination of benzoic acid and adipic acid, carboxylic acids and ethoxylated amines, or aliphatic monocarboxylic acid and aliphatic dicarboxylic acid, as nucleating agents for polyolefins are described in U.S. Pat. Nos. 4,704,421, 4,829,114, 5,300,549, 5,319,012 and 5,491,187.
Polyolefins have also become commercially important in the manufacture of polyolefin composites, such as polyethylene and polypropylene composites, for various applications. Composite properties are often improved considerably due to the use of fillers such as glass fibers in polyolefins. In order to assist the fibers to adhere to the polyolefin matrix and to protect fibers during processing, glass fibers are usually coated with an aqueous sizing composition. One way to help distribute the aforementioned solid nucleating agents evenly in polyolefins is to let the fillers carry and deliver the nucleating agents throughout the polyolefin matrix.
Glass fibers intended for incorporation as reinforcing elements in articles fabricated from various resinous materials, such as polyolefins, are usually coated with sizing compositions to protect fibers from damage during processing and to enhance the interaction between the fibers and the polymeric matrix. Such sizing compositions typically contain a film forming polymer, a lubricant, a coupling agent, and other ingredients known to those skilled in the art, all dispersed or dissolved in an aqueous medium. The film forming polymer is usually compatible with the matrix resin in which the glass fibers are embedded as reinforcement. A broad range of oils, waxes, etc., have been used as lubricants. Among the widely used coupling agents are organosilanes (e.g. Silquest® A1001, an aminosilane from Crompton Corporation).
Other components such as antifoam agents, pH regulators, surfactants, and UV stabilizers are also frequently included in such sizing compositions. Various aqueous sizing compositions for glass fibers have been reported in U.S. Pat. Nos. 4,394,414, 4,448,911, 4,656,084, 5,130,197 and 5,646,207. The aforementioned normally solid nucleating agents when coated on glass fibers are capable of enhancing nucleation in polyolefin matrices thereby improving the clarity and mechanical properties of the glass fiber reinforced polyolefin composites.
It is therefore highly desirable to provide nucleating agents in an aqueous form which is compatible and miscible with aqueous sizing compositions. The advantage of using an aqueous dispersion of nucleating agents of this invention in preparing sizing compositions to coat glass fibers with the resultant improvement in polyolefin composite properties of the glass fiber reinforced polyolefins have not heretofore been appreciated in the art.
It is an object of the present invention to provide stable and pumpable aqueous dispersions of normally solid nucleating agents.
Another object of the present invention is the process of making the aqueous dispersion of nucleating agents.
Also an object of the present invention is the method of using aqueous nucleating agent dispersion in aqueous sizing composition for glass fibers. Another object of the present invention is the method of using the sized glass fibers in polyolefin composites having improved mechanical properties. Other objects will become apparent from the ensuing description.